Many computer guided orthopaedic surgical procedures are based on determining the position of bones, and relating this position to the computer via some type of ultrasonic, magnetic resonance, or optical sensor. In such cases, a first sensor may be secured to the patient's bone, with a second sensor being secured to the surgical instrument so that the instrument may be subsequently guided via a computer into the desired position within the patient's bone. U.S. Patents and Patent Publications relating to computer guided surgery include U.S. Pat. No. 5,520,694 and U.S. Patent Application Publication Nos. 2003/0153978 A1 and 2003/01538829 A1, each of which is hereby incorporated by reference. Similar computer-assisted navigation systems are disclosed in U.S. Pat. Nos. 6,514,259; 6,434,507; 6,428,547; 6,424,856; 6,351,659; 6,223,067; 6,187,018; 6,178,345; 5,889,834; 5,769,861; 5,702,406; 5,643,268; and 5,628,315, along with U.S. Patent Application Publication No. 2002/0038118 A1, each of which is hereby incorporated by reference.